JEE Main & Advanced Mathematics Sequence & Series Question Bank nth term of special series, Sum to n terms and Infinite number of terms

  • question_answer
    \[\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+........+.......\frac{1}{n.(n+1)}\]equals [AMU 1995; RPET 1996;  UPSEAT 1999, 2001]

    A)   \[\frac{1}{n(n+1)}\]

    B) \[\frac{n}{n+1}\]

    C)   \[\frac{2n}{n+1}\]

    D) \[\frac{2}{n(n+1)}\]

    Correct Answer: B

    Solution :

    \[\left( \frac{1}{1}-\frac{1}{2} \right)+\left( \frac{1}{2}-\frac{1}{3} \right)+\left( \frac{1}{3}-\frac{1}{4} \right)+.........+\left( \frac{1}{n}-\frac{1}{n+1} \right)\] \[=1-\frac{1}{n+1}=\frac{n}{n+1}\].


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